This invention relates to a gaseous fuel cell. More specifically, it relates to the use of a novel solid electrolyte and a catalyst in producing electricity from hydrogen or gases capable of dissociating to yield hydrogen ions.
The Nernst equation provides a mathematical description of such a system, as follows. When two media with different partial pressures, P.sub.1 and P.sub.2, of a particular substance present in both media are separated by a solid electrolyte (ionic conductor) and conducting electrodes are attached to both sides of the ionic conductor, an EMF is generated which is related to the partial pressures as follows: ##EQU1## where R is the gas constant, T is absolute temperature, F is the Faraday constant, E.sub.o is the standard oxidation-reduction potential difference, EMF is electromotive force, and n is the number of electrons per molecule of product from the overall cell reaction. If the system described by the above equation behaves non-ideally, the partial pressures must be replaced by fugacities. Another factor which may need to be considered in regard to a particular system is the rate of dissociation to form the ions which pass through the solid electrolyte. This may be a limiting factor to the transfer of ions through the electrolyte. The rate of dissociation can be calculated by means of the equilibrium constant for the dissociation reaction.
In a simple hydrogen-oxygen fuel cell, the fuel gas is hydrogen and the oxidant gas is oxygen. Hydrogen dissociates into hydrogen ions and electrons at the catalyst on the fuel gas side of the membrane. The hydrogen ions pass through the electrolyte element while the electrons flow through the external circuit, doing electrical work before forming water by combining with, at the catalytic agent on the oxidant gas side of the membrane, hydrogen ions which passed through the membrane and oxygen. A flow of gases is normally maintained for continuous operation of the fuel cell. The maximum voltage which can be produced by a fuel cell is a thermodynamic function of the fuel and oxidant. For a hydrogen-oxygen fuel cell at STP, the theoretical EMF is 1.23 volts. The actual voltage will be less due to losses within the cell. The current produced is controlled by such considerations as the rate at which the electrochemical reactions proceed, the electrolyte thickness, and the catalyst surface area. In a simple hydrogen-oxygen cell, the partial pressure term of the Nernst equation becomes partial pressure of water divided by the quantity partial pressure of hydrogen times square root of partial pressure of oxygen.
A novel solid electrolyte membrane is used in the present invention. We have discovered that a polymer blended membrane may be fabricated by admixing a heteropoly acid or a salt thereof with an organic polymer which is at least partially compatible with said heteropoly acid or salt to form a polymer blended composition of matter which is useful in gas detection. It was totally unexpected that a thin film membrane could be cast from such a blend to provide a membrane which would be highly selective to certain gases and therefore able to act as a proton conductor in a fuel cell where molecular hydrogen is converted into protons on one side of the device, transported through the membrane, and recombined as molecular hydrogen on the other side. The membrane is also useful with gases capable of dissociating into hydrogen ions. For background information relating to this aspect of the present invention, reference may be made to the book Solid Electrolytes and Their Applications, edited by Subbarao, Plenum Press, 1980. For information on fuel cells see Journal of the Electrochemical Society, March, 1978, p. 77C and U.S. Pat. No. 3,403,054 (Puffer et al.).